68 PLANT GEOGRAPHY 



brought in ships' ballast, in the straw of packing-cases, 

 or in foreign wool or hay, or escaping from gardens, but 

 unable to hold their own, are known as casuals. Many 

 of these may, of course, be repeatedly re-introduced. 

 Weeds of cultivated ground, many of which may be of 

 ancient introduction, though showing their foreign origin 

 by not passing beyond the limits of cultivation and, 

 perhaps, by imperfect adaptation to the climate, are 

 termed colonists. Such are our Poppies, Corn-marigold 

 (Chrysanthemum segetum L.), Corn-crowfoot (Ranunculus 

 arvensis L.), etc., species remarkable for the profusion 

 of their seed-production. Veronica Buxbaumii Tenore, 

 first recorded in Britain in 1829, may be termed a 

 colonist. On the other hand, apparent escapes from 

 cultivation that have so far established themselves, or 

 become naturalised, as to be able to spread away from 

 cultivation like native species, reproducing themselves 

 freely, are known as denizens. Among British examples 

 we may mention Chelidonium majus L., Myrrhis odorata 

 L., and the American Impatiens bi flora Walt., first 

 recorded in Surrey in 1822; Elodea canadensis Michx., 

 dating from about 1842; Claytonia perfoliata Donn, of 

 somewhat earlier date; Galinsoga parvi flora Cav., which 

 apparently escaped from Kew Gardens about 1850; and 

 Mimulus Langsdorfii Donn. 



KRAKATAU. The relative importance of the different 

 agents of plant-dispersal has been interestingly illus- 

 trated in the re-stocking of the volcanic island of Krakatau 

 after its devastation by the eruption of 1883. Other 

 islands are from twelve to twenty-three miles distant, 

 strong monsoon winds blow from opposite directions, 

 and the ocean-currents are not constant in direction. 

 Within three years many wind-carried species of blue- 

 green Algae, Diatoms, and Bacteria had established 

 themselves on the pumice and ash of the mountain- 

 slopes, and Ferns, with their light spores, preponderated 

 among the larger plants, far outstripping the sea-borne 

 strand -plants. Ten years later various Grasses, Cyperacea, 

 and Orchids had been added to the list of wind-borne 

 species, which constituted 16-30 per cent, of the whole 

 number of Phanerogams ; and 1 6 species of Ferns were 

 recorded ; while fully 39 per cent, of the flowering-plants 

 were sea-borne species. Large piles of floating trees, 

 stems, branches, and Bamboos were met with on the 



